They will give you a set of boosters for you to keep. And from those booster packs, you make your own deck to compete with everyone else. And depending on the number of persons who signed up, the prize could differ.

That sounds like fun! Is there a buy in or something for the cards, or do they give them promotionally? I would like to get some more PS and BC while I'm there, so I gotta make sure I have enough cash.